Question: The lifespans of turtles in a particular zoo are normally distributed. The average turtle lives $106$ years; the standard deviation is $19$ years. Use the empirical rule (68-95-99.7%) to estimate the probability of a turtle living less than $144$ years.
Answer: $106$ $87$ $125$ $68$ $144$ $49$ $163$ $95\%$ $2.5\%$ $2.5\%$ We know the lifespans are normally distributed with an average lifespan of $106$ years. We know the standard deviation is $19$ years, so one standard deviation below the mean is $87$ years and one standard deviation above the mean is $125$ years. Two standard deviations below the mean is $68$ years and two standard deviations above the mean is $144$ years. Three standard deviations below the mean is $49$ years and three standard deviations above the mean is $163$ years. We are interested in the probability of a turtle living less than $144$ years. The empirical rule (or the 68-95-99.7 rule) tells us that $95\%$ of the turtles will have lifespans within 2 standard deviations of the average lifespan. The remaining $5\%$ of the turtles will have lifespans that fall outside the shaded area. Because the normal distribution is symmetrical, half $({2.5\%})$ will live less than $68$ years and the other half $({2.5\%})$ will live longer than $144$ years. The probability of a particular turtle living less than $144$ years is ${95\%} + {2.5\%}$, or $97.5\%$.